Thermally stable fuel composition

ABSTRACT

Thermally stable light distillate turbine fuel composition containing 1) a substituted carbamate and 2) an aldehyde-amine condensation product, and a method for operating a turbine engine.

States Patent Unite Bialy et al.

[451 Mar. 28, 1972 [54] THERMALLY STABLE FUEL COMPOSITION [72] Inventors: Jerzy J. Bialy; Peter Darn, both of Lagrangeville, N.Y.

[73] Assignee: Texaco Inc., New York, N.Y.

[22] Filed: May 15, 1970 [21] Appl. No.: 37,914

52 us. Cl ..44/71, 252 403 [58] Field of Search ..44/71, 73; 252/403 3,034,876 5/1962 Geeetal 3,071,451 l/l963 Schmerling....

Primary Examiner-Daniel E. Wyman Assistant Examiner-W. J. Shine Attorney-Thomas H, Whaley and Carl G. Reis [5 7] ABSTRACT Thermally stable light distillate turbine fuel composition eonn taining l) a substituted carbamate and 2) an aldehyde-amine condensation product, and a method for operating a turbine engine.

4 Claims, No Drawings THERMALLY STABLE FUEL COMPOSITION BACKGROUND OF THE INVENTION 1. Field of the Invention It is recognized that kerosene base distillate petroleum hydrocarbon fuel compositions maintained at high temperatures are susceptible to thermal degradation and oxidation to produce a suspension of finely divided insoluble bodies in the fuel and the formation of deposits on heat exchanging surfaces. The degree that these undesirable changes take place is dependent on the amount of unstable constituents present in the oil and on the temperature stress and oxidation conditions to which the oil is subjected. The thermal stability rating of fuel compositions of the type in question is determined in a Fuel Coker Test more fully described hereinbelow.

The problem of thermal stability is particularly serious for light hydrocarbon oils in the kerosene boiling range which must be maintained at a relatively high temperature for extended periods of time in intimate contact with an oxygencontaining atmosphere. Kerosene base turbine fuels are maintained in such an environment in the wing tanks of aircraft. This problem becomes more acute for fuel compositions designed to fuel aircraft having speeds in the Mach 2 and 3 speed ranges or above, as is projected for the forthcoming supersonic transports, because of the substantially higher wing tank temperatures generated.

When a turbine or jet fuel has insufficient thermal stability, degradation takes place, one effect being the formation in the fuel of a suspension of finely divided insoluble bodies. These insoluble bodies are separated from the fuel in the fuel filters of the engine. If there are excessive amounts of insoluble bodies present in the fuel, the fuel line filters become partially or completely blocked resulting in seriously curtailed or lost engine power due to fuel starvation.

The tendency toward deposit formation in a thermally unstable fuel causes a deposits build-up or coking phenomenon commonly referred to as heater tube deposits. This deposits formation seriously interferes with the operation of the fuel-oil heat exchanger in an airplane. It is recognized that a build-up of heater tube deposits cuts down on the heat exchanging efiiciency, causes lubricating oil overheat and can lead to engine failure. In supersonic aircraft, the heat exchanger requirements are further increased because of the need to cool the passenger and crew compartments.

DESCRIPTION OF THE PRIOR ART AND RELATED COPENDING APPLICATION (S) US. Pat. No. 3,071,451 discloses a class of aldehyde-amine condensation products which are effective as metal deactivators in gasoline and oil compositions. In general, these products are N,N'-di(3-alkenylsalicylidene)-diaminoalkanes.

US. Pat. No. 2,842,433 discloses a class of polyglycol carbamates which are effective as inhibitors against the formation of combustion chamber deposits in internal combustion reciprocating gasoline engines.

A copending application Ser. No. 822,734 filed on May 7, 1969 discloses a thermally stable turbine fuel composition containing a heteropolymer of ethylene, a C to C olefin and optionally a higher olefin in combination with an aldehydeamine condensation product.

SUMMARY OF THE INVENTION The fuel composition of the invention comprises a mixture of hydrocarbons in the kerosene boiling range comprising (1) a substituted carbamate and (2) an aldehyde-amine condensation product. More particularly, a light distillate fuel oil composition is provided containing from about 0.0005 to 0.1 weight percent of a substituted carbamate represented by the formula:

in which R is hydrogen or an aliphatic hydrocarbyl radical having from one to 18 carbon atoms, R is an aliphatic hydrocarbyl radical having from one to 18 carbon atoms and n is an integer from 1 to 3, or the formula:

in which R and R have the values noted above and R" is an aliphatic hydrocarbyl radical having from one to eight carbon atoms, and from about 0.0003 to 0.0l weight percent of an aldehyde-amine condensation product represented by the formula:

in which R is hydrogen or an aliphatic hydrocarbyl radical having from one to 18 carbon atoms, R is an aliphatic hydrocarbyl radical having from one to 18 carbon atoms and n is an integer from one to 3, or a carbamate having the formula:

in which R and R have the values noted above and R" is an aliphatic hydrocarbyl radical having from one to eight carbon atoms.

Typical glycol carbamates of the invention include for example: diethylene glycol bis( N,N-diallyl carbamate diethylene glycol bis( N,N -2-ethylhexyl carbamate diethylene glycol bis( N,N'-dipropargyl carbamate diethylene glycol bis(N,N'-allyl carbamate); diethylene glycol bis [N,N'-di-(l-methylisopentyl) carbamate]; diethylene glycol bis(N,N'-n-propyl carbamate); diethylene glycol bis- (N,N-diisopropyl carbamate); triethylene glycol bis(N,N'-diallyl carbamate); triethylene glycol bis(N,N-dioctadecyl carbamate); triethylene glycol bis(N,N'-dimethyl carbamate); triethylene glycol bis [N,N-( l,l-dimethyl-2-propynyl) carbamate]; tetraethylene glycol bis(N,N-2X-ethylhexyl carbamate); tetraethylene glycol bis(N,N'-allyl carbamate); pentaethylene glycol bis(N,N'-propargyl carbamate); pentaethylene glycol bis(N,N'-n-propyl carbamate); hexaethylene glycol bis(N,N'-diallyl carbamate); hexaethylene glycol bis(N,N'-butyl carbamate); and hexaethylene glycol bis(N,N'-2-ethylhexyl carbamate).

Typical carbamates include N-C sec. alkyl-n-butyl carbamate, N,N-dioctyl-n-butyl carbamate, N,N-dihexyl-noctyl carbamate, N-stearyl-2-ethylhexyl carbamate, N,N'- dilauryl-amyl carbamate and N-dodecyl-propyl carbamate.

The substituted carbamate is generally employed in the fuel composition in a concentration ranging from about 0.0005 to 0.1 weight percent with the preferred concentration of this component being in the range of 0.001 to 0.005 weight percent, the latter amounts corresponding to about 3 and 15 ptb (pounds per thousand barrels).

The metal deactivator component of this invention is an aldehyde-amine condensation product represented by the forin which R is a divalent hydrocarbyl radical having from two to four carbon atoms and R is hydrogen or an aliphatic hydrocarbyl radical having from one to six carbon atoms. Examples of typical deactivators are N,N-disalicylidene-l,2- propanediamine and N,N-disalicylidene-1,2-ethanediamine, N,N-disalicylidene-1,2-butanediamine, N,N'-di( 3-alkenylsalicylidene )-l ,2-propanediamine, N,N-di( 3-allyl-salicylidene l ,2-propanediamine, N,N '-di( 3-methallyl-salicylidene)-l,2-propanediamine and N,N'-di-[3-(2 hexenyl) salicylidene1-l,2-propanediamine. The metal deactivator is employed in the fuel at a concentration ranging from about 0.0003 to 0.0] weight percent which corresponds to about 0.8 and 28 ptb respectively.

The base fuel of the invention is a hydrocarbon or mixture of hydrocarbons boiling in the kerosene boiling range. in general, these base fuels boil at a temperature ranging from The base fuel employed in these tests was a kerosene base turbine fuel having the following properties:

Luminometer Number 53 The efiectiveness of the additives of the invention in the above turbine base fuel is shown by the Fuel Coker Test results set forth in the table below. The concentration of the additive components in the additive-containing fuels is shown in ptb (pounds per thousand barrels of the fuel composition).

TABLE I.ASTM COKER THERMAL STABILITY TEST [Temperature, preheater/filter, 450/550 F.]

N,N- Rating disalicylidene- Conc 1.2-propane- Pre- Filter P, Time, Run Base luel plus carbamate derivative P'IB diamine, PIB heater in. Hg 2 min.

1 Base fuel 3 25 97 2 .do 4 25 218 3 .dO 3 3 26 105 4 Diethylene glycol-bis(N,N-ally1 carbamate) 4 25 218 5 d 20 3 l 1.2 300 6 Diethylene glyc0l-bis(N ,N-n-0ctyl-carbamate) 20 3 2 0.7 300 7 Diethylene glyc0l-bis(N,N-C1 -;4 sec. alkyl carbamate) 20 3 0 4. 300 8 N-Cm 4 sec. alkyl-n-butyl carbamate 3 1 0.5 300 l Preheater rated from 0good to 4-bad (a rating of 2 or less passes). 1 Filter rating is the pressure in inches of mercury across the filter recorded at the conclusion of the test (300 minutes). If the pressure reaches inches of mercury the test is terminated t that time.

about 325 to 625 F., and preferably from about 350 to 550 F. Fuel compositions for turbine engines containing a substantial proportion of hydrocarbons in the gasoline boiling range, such as JP-4, a mixture of about 70 percent gasoline and percent light distillate having a 90 percent evaporated point of 470 F., have a high level of thermal stability and are not significantly improved by the additive combination of this inventron.

The preparation of the turbine or jet fuel composition of the invention simply involves the addition of the two component additive to the fuel in the indicated amounts.

The effectiveness of the fuel compositions of the invention was determined by preparing typical jet fuel compositions and testing for thermal stability in the CFR Fuel Coker Test (ASTM-D-660-6 l -T).

An important indication of the thermal stability of a fuel composition is the temperature level at which the fuel performs satisfactorily. The fuel flow employed in the test was a rate of 6 lb. per hour for 5 hours (300 minutes). if the back pressure caused by filter plugging reaches 25.0 inches of mercury before 300 minutes elapses, the fuel fails this test. For

military purposes, a filter pressure of less than 12.0 inches of mercury in 300 minutes is satisfactory (see MIL-J-5624F). The deposits formed on the tube are rated as from 0 to 4 (where 0 best; 4 worst) depending on the extent of the deposit formation on the tube. A tube rating of 2 or less is satisfactory and a rating greater than 2 fails.

in which R is hydrogen or an aliphatic hydrocarbyl radical having from one to 18 carbon atoms, R is an aliphatic hydrocarbyl radical having from one to 18 carbon atoms and R" is an aliphatic hydrocarbyl radical having from one to eight carbon atoms, and (2) from about 0.0003 to 0.01 weight percent of an aldehyde-amine condensation product having the formula:

6 in which R is a divalent hydrocarbyl radical having from two 3. A fuel composition according to claim 1 in which said to four carbonamms y f an aliphatic substituted carbamateisN,N'-dioctyl-n-butylcarbamate. hydrocarbyl radical having from one to eight carbon atoms. 4' A fuel composition according m claim 1 in which said 2. A fuel composition according to claim 1 containing N- C sec.-alkyl-n-butyl carbamate and N,N'disalicylidene- 1,2-propanediamine.

5 substitut ed carbamate is N,N'-dihexyl-n-octyl carbamatc. 

2. A fuel composition according to claim 1 containing N-C10 14sec.-alkyl-n-butyl carbamate and N,N''disalicylidene-1,2-propanediamine.
 3. A fuel composition according to claim 1 in which said substituted carbamate is N,N''-dioctyl-n-butyl carbamate.
 4. A fuel composition according to claim 1 in which said substituted carbamate is N,N''-dihexyl-n-octyl carbamate. 